Method of determining the lubrication mechanism in cmp

ABSTRACT

The present invention is a method for obtaining data easily, accurately and effectively that may be used in determination of Sommerfeld Numbers and COF for CMP polishing. Using the Sommerfeld Numbers and COF values thus obtained the lubrication mechanism of CMP polishing with particular materials and under particular conditions can easily and reliably be studied. The method of the present invention is accomplished by use of CMP polishing tools capable of simultaneously measuring shear force and normal force, and rendering a value for the COF while simultaneously enabling the operator to change pressure on and relative velocity of the CMP wafer and CMP polishing pad in real time. Using the said CMP tool, the pressure and relative velocity may be varied separately or together for the desired length of time according to the needs of the operator so that within one CMP process multiple measurements may be taken under the same process conditions.

FIELD OF THE INVENTION

In chemical mechanical planarization, one area that can potentiallyimpact inter-layer dielectric removal rates is the coefficient offriction associated with the pad, wafer, and slurry abrasive particles.To understand the dominant tribological mechanism present when polishinginterlayer dielectrics, Stribeck curves are presented using adimensionless grouping of CMP specific parameters, called the Sommerfeldnumber.

So=μU/pδ _(eff)

where μ is the slurry viscosity, U is the relative pad-wafer velocity, pis the applied wafer pressure, and δ_(eff) is the effective fluidthickness. Determination of μ and U are fairly straightforward as can bemeasured experimentally for a given slurry and U depends upon toolgeometry and the relative angular velocity of the platen and wafer.

Wafer pressure is the applied downforce divided by the contact areabetween the wafer and the pad. Each pad type consist of a differentsurface area due to different grooving configurations, so each pad willexperience a different pressure when subjected to the same normal force.To account for this a dimensionless parameter, α is determined for eachpad type equal to the ratio of the total up (raised) area of the pad andthe total flat surface area of the pad. The determination of actualpressure experienced by the wafer is 1/α multiplied by the appliedpressure. The δ_(eff) may moreover be calculated using this α in thefollowing formula¹

δ_(eff) =α×R _(a)+(1−α)×δ_(groove)

The coefficient of friction is defined as the quotient of the shearforce and the normal force. The plot of the coefficient of frictionversus the Sommerfeld number is known as either the Stribeck-Gumbelcurve or the McKee Petroff Curve and will be referred to herein as the“Stribeck curve”.² Recent research has indicated, however, that δ_(eff)may be closely quantified as R_(a).³ ¹ Ara Philipossian and Scott Olsen,Fundamental Tribological and Removal Rate Studies of Inter-layerDielectric Chemical Mechanical Planarization. Jpn. J. Appl. Phys. Vol.42 (2003) pp. 6371-6379 hereinafter totally incorporated by reference.²Ibid.³ “Determining the Effects of Slurry Surfactant, Abrasive Size, andAbrasive Content on the Tribology and Kinetics of Copper CMP” by Z. Li,K. Ina, P. Lefevre, I. Koshiyama and A. Philipossian. J. Electrochem.Soc., 152 (2005) G299-G304 hereinafter totally incorporated byreference.

The Stribeck curve is useful in CMP for providing evidence of the extentof contact between the rotating wafer, the rotating pad and the abrasiveparticles. Three major areas of the Stribeck curve can be distinguished:boundary lubrication at small Sommerfeld numbers where all solid bodiesare in intimate contact with each other, mixed lubrication where thewafer and pad are not in intimate contact but some abrasives remain incontact and a thin fluid film about the thickness of the roughness ofthe pad forms, and hydrodynamic lubrication at large Sommerfeld numberswherein the fluid film between pad and wafer is larger than theroughness of the pad.⁴ ⁴ Ibid.

Use of the Stribeck curve can demonstrate what lubrication conditionscorrespond to what pressure and velocity conditions for a particularpad. Not only is this very useful for characterising the properties ofCMP consumables (i.e., polishing pads, slurries and conditioner discs)but also for studying the tribological mechanism for specific pads andslurries and for determining or comparing optimal or other CMP processconditions.

Determination of the Stribeck curve heretofore has involved thedetermination of COF by measuring shear force in real time with a setnormal force that could only be changed by stopping the operation andresetting the load on the wafer and then starting again. In addition tobeing time consuming, there was also the problem that having stopped arun, it would not be a straightforward matter of starting a subsequentrun and obtaining consistent conditions. The necessity of stopping theCMP process to adjust the load was a major problem in the prior art.

In Fundamental Tribological and Removal Rate Studies of Inter-LayerDielectric Chemical Mechanical Planarization by Philipossian and Olsen⁵hereinafter totally incorporated by reference, plotting of StribeckCurves for specific wafer, pad and slurry combinations was accomplishedby use of a scaled polisher capable of measurement of the shear force inreal and capable of alteration of the speed of rotation of the wafer andpad during operation. However, there was no direct measurement of thenormal force and change in pressure required the process to be stoppedand the pressure changed. Although it was possible to construct StribeckCurves for a number of points based on change in relative velocityalone, it was not possible to do so easily or consistently for change inpressure and both pressure and relative velocity could not be altered atthe same time or within the same operational sequence. From the StribeckCurve it is possible to determine accurately the mechanism oflubrication consequently of wear in CMP polishing procedures forparticular wafers, pads and under particular conditions. ⁵ Ibid.Philipossian Olsen, (2003) pp. 6371-6379

SUMMARY OF THE INVENTION

The present invention relates to a method for obtaining data to generatethe Stribeck curve and consequently the lubrication mechanism in CMPpolishing processes in which both pressure between the polishedsubstrate and polishing pad and relative velocity of the surfaces may bealtered in real time during the same CMP processing operation and thenormal force component of the coefficient may be measured directly andaccurately during the CMP polishing process. More specifically themethod of the present invention is accomplished by use of a CMPpolishing tool according to U.S. patent application Ser. No. 12/254,291,and more specifically a CMP polishing tool that determines and reportsthe shear force between the polished substrate and the polishing padwherein the said determination is accomplished by means of a platepositioned above the wafer head and from which the wafer head and itssupporting apparatus hang, or upon which they rest, said plate connectedto the framework of the CMP polishing tool by low friction motion meanscapable of sliding in a direction perpendicular to the line between thecenter of the polishing pad and the center of the wafer head, and a loadcell sensor firmly fixed to the framework of the CMP polishing tool orother immovable structure and positioned to contact and determine theforce from the leading edge of said plate when the CMP polishing tool isin operation and the wafer head is in contact with the polishing pad,the signals thus obtained reporting the shear force and additionally inwhich load cells are attached to and support the bottom of the module ofthe polishing pad of the CMP polishing tool to determine the normalforce, and the normal force and shear force thus obtained may be used tocalculate the coefficient of friction between the wafer head and thepolishing pad. Further, the said CMP tool is capable of alteration ofthe pressure and relative velocity during operation by means of steppingmotors and a device for the variation of load on the wafer during theCMP polishing procedure. Using the said CMP tool, the pressure andrelative velocity may be varied separately or together for the desiredlength of time according to the needs of the operator so that within oneCMP process several measurements may be taken. However, change in loadand consequently changes of pressure in the apparatuses and methods ofthe prior art could only be accomplished by stopping the CMP polishingprocess and manually changing the load on the wafer or the apparatus andthere was no means by which to directly measure the normal force whichthen had to be estimated.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph of measurement of the Shear Force, Normal Force andCOF measured during a CMP polishing operation during which pressure andrelative velocity were varied by specific amounts at specific intervals.

FIG. 2 is a graph of measurement of the Shear Force, Normal Force andCOF measured during a CMP polishing operation during which pressure andrelative velocity were varied by specific amounts at specific.

FIG. 3 is the Stribeck Curve for FIG. 1.

FIG. 4 is the Stribeck Curve for FIG. 2.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

The inventor(s) of the present invention, in order to solve the problemof obtaining data for the determination of a Stribeck curve thatdescribes the lubrication mechanism for a CMP process using a certainpolishing pad, wafer and slurry without having to stop and restart theprocess to change the pressure and which accurately provides data on thenormal force, have with considerable effort and investigation developedthe method of the present invention.

More particularly they have devised a method of determination of aStribeck curve using a CMP polishing tool according to U.S. patentapplication Ser. No. 12/254,291, and more specifically a CMP polishingtool that determines and reports the shear force between the wafer headand the polishing pad wherein the said determination is accomplished bymeans of a plate positioned above the wafer head and from which thewafer head and its supporting apparatus hang, or upon which they rest,said plate connected to the framework of the CMP polishing tool by lowfriction motion means capable of sliding in a direction perpendicular tothe line between the center of the polishing pad and the center of thewafer head, and a load cell sensor firmly fixed to the framework of theCMP polishing tool or other immovable structure and positioned tocontact and determine the force from the leading of said plate when theCMP polishing tool is in operation and the wafer head is in contact withthe polishing pad, the signals thus obtained reporting the shear forceand additionally in which load cells are attached to and support thebottom of the module of the polishing pad of the CMP polishing tool todetermine the normal force, and the normal force and shear force thusobtained may be used to calculate the coefficient of friction betweenthe wafer head and the polishing pad. Further, the said CMP tool iscapable of alteration of the pressure and relative velocity duringoperation by means of stepping down devices and a device for thevariation of load on the wafer during the CMP polishing procedure. Usingthe said CMP tool, the pressure and relative velocity may be variedseparately or together for the desired length of time according to theneeds of the operator so that within one CMP process severalmeasurements may be taken.

The method of the present invention has been developed in response tothe present state of the art, and in particular, in response to theproblems and needs in the art that have not yet been fully solved bycurrently available CMP methods for measurement of data fordetermination of lubrication mechanism in CMP. Thus, it is an overallobjective of the present invention to provide a method for determinationof the lubrication mechanism in CMP and more particularly in theeffective acquisition of data for the plotting of Stribeck curves thatremedy the shortcomings of the prior art.

The purpose of the method of the present invention is to allowsignificantly more accurate and more convenient determination of theStribeck curve for CMP polishing between the wafer and relatedstructures and the CMP polishing pad and by extension to permitsignificantly more effective, accurate and convenient determination ofthe lubrication mechanism of CMP.

Through the use of the method for determining the lubricating mechanismin CMP of the present invention, a more accurate, effective andconvenient observation of the COF relationship to variation in pressureand relative velocity between the wafer and the CMP polishing pad may berapidly obtained with a minimum of error. Furthermore, this method maybe easily and cost-effectively applied to facilitate and enhance the useof CMP polishing tools and the polishing pads used in them. These andother features and advantages of the present invention will become morefully apparent from the following description and appended claims, ormay be learned by the practice of the invention as set forthhereinafter.

The method of the present invention comprises measuring the shear forceand normal force between a wafer and a CMP polishing pad on a CMPpolishing tool in which the pressure between the wafer and the relativevelocity of the wafer and CMP polishing pad may be independently andprecisely varied, and to sequentially vary the said pressure, relativevelocity or both at set intervals sufficient to obtain a reading forshear force, normal force and COF. This data may be analyzed and the COFvalues and Stribeck curve determined and output by data processing meanssuch as a computer.

The CMP polishing tool used in the method of the present invention isnot particularly limited, provided however, that it should be possibleto measure at the shear force in at least one direction and to measurethe normal force during polishing and to change precisely duringoperation the load on the wafer and the rate of rotation of at least thepolishing pad and preferably the rate of rotation wafer as well. It ispreferred that the CMP polishing tool of the present invention iscapable of measuring shear force in two component directions. Morepreferably, the CMP polishing tool of the present invention possesses aplate positioned above the wafer head from which the wafer head and itssupporting apparatus hang, or upon which they rest, said plate connectedto the framework of said CMP polishing tool by low friction motion meanscapable of sliding in a direction perpendicular to the line between thecenter of the polishing pad and the center of the wafer head, and a loadcell sensor firmly fixed to the framework of the CMP polishing tool orother immovable structure and positioned to determine contact anddetermine force from the leading edge of said plate when the CMPpolishing tool is in operation and the wafer head is in contact with theCMP polishing pad, the signals thus obtained reporting the shear forceand in which load cells are attached to and support the bottom of theCMP polishing pad module of the CMP polishing tool to determine thenormal force, and the shear force and the normal force thus obtained maybe used to calculate the coefficient of friction in accordance with U.S.patent application Ser. No. 12/254,291 hereby totally incorporated byreference.

Even more preferably, the CMP polishing tool of the present inventiondetermines two perpendicular force components of shear force and theresulting shear force by means of two plates positioned above the waferhead from which the wafer head and its supporting apparatus hang, orupon which they rest, one plate connected to the framework of said CMPpolishing tool by low friction motion means, the other said plateconnected to the first said plate by low friction motion means allowingthe said other plate to slide in a direction perpendicular to the motionof the first said plate and load sensor cells firmly fixed to theframework of the CMP polishing tool or other immovable structure andpositioned to determine contact and determine force from the leadingedge of said plate when the CMP polishing tool is in operation and thewafer head is in contact with the CMP polishing pad, and reports thesaid perpendicular force components as signals and in which load cellsare attached to and support the bottom of the CMP polishing pad moduleof the CMP polishing tool to determine the normal force, and the shearforce and the normal force thus obtained are used to calculate thecoefficient of friction in accordance with U.S. patent application Ser.No. 12/254,291.

Yet even more preferably, the CMP polishing tool of the presentinvention determines two perpendicular force components of shear forceand the resulting shear force by means of two plates positioned abovethe wafer head from which the wafer head and its supporting apparatushang, or upon which they rest, one plate connected to the framework ofsaid CMP polishing tool by low friction rails, the other said plateconnected to the first plate by low friction rails allowing the othersaid plate to slide in a direction perpendicular to the motion of thefirst said plate, load cells sensor firmly fixed to the framework of theCMP polishing tool or other immovable structure and positioned tocontact and determine force from the leading edge of said plate when theCMP polishing tool is in operation and the wafer head is in contact withthe polishing pad, the signals of the load cell sensors thus obtainedreporting the components of shear force, and in which load cell sensorsare attached to and support the bottom of the CMP polishing pad moduleof the CMP polishing tool to determine the normal force, and the shearforce and the normal force thus obtained are delivered to a dataprocessing means to calculate the coefficient of friction in accordancewith U.S. patent application Ser. No. 12/254,291.

The means of alteration of the relative velocity between the CMP waferand the CMP polishing pad during CMP polishing are not particularlylimited but stepping down and variable velocity apparatus incorporatedinto the polishing tool for that purpose either as commerciallyavailable or by subsequent modification are preferred. The means ofalteration of the pressure between the CMP wafer and the CMP polishingpad during CMP polishing are not particularly limited and any suitablemeans such as mechanical screws, solenoids, hydraulic systems and thelike may be employed either in the system as purchase commercially or assubsequently modified.

Using the aforementioned apparatuses, the relative motion of the wafermay be calculated from the rotation speed of the CMP polishing pad andwafer carrier. If the rotation rate of pad and wafer are significantlydifferent, than the relative motion of wafer has to take into accountboth rotation rates. The pressure between the wafer and pad iscalculated by dividing the load applied to the wafer by the area of thewafer in contact with the CMP polishing pad. The components of shearforce and the normal force are obtained directly from the sensors.Calculation may be accomplished manually but use of signal data incalculation by a data processor such as a computer with softwareprepared for that purpose is preferred.

Any wafer that may be used in CMP polishing may be used in the presentinvention including without limitation wafers with surfaces of copper,aluminium, tungsten, silicon dioxide and the like. Patterned wafers mayalso be used. Likewise, any polishing pad that may be used in CMPpolishing may be used in the present invention. The conditions of theCMP polishing operation that may be employed are not particularlylimited and conditions that are normally used in CMP polishing ofvarious types of CMP wafers may be used. The length of the CMP polishingrun is not particularly limited but between 30 seconds and 3 minutes ispreferred. Conditioning pads may be used to roughen the surface of theCMP polishing pad during CMP polishing. The temperature at which the CMPpolishing process is carried out is not limited but between 10 degreesand 45 degrees centigrade is preferred and room temperature is morepreferred.

The type of slurry used in the present invention is not particularlylimited and any slurry applicable to CMP polishing may be used includingwithout limitation any commercially available alumina, silica or ceriaslurry. Since the viscosity of the slurry has not been regarded aschanging significantly under conditions of the present invention, it maybe regarded as constant for purposes of the present invention; however,it may be desirable to determine the viscosity of the slurry for thepurpose of more detailed reporting of the relationship between theresulting COF data and the relative velocity of the wafer and CMPpolishing pad and the pressure between them. There is no one tool thatcan provide this information but a combination of tools and techniquesthat can render the determination of local viscosity as accurately aspossible is preferred. The viscosity of commercial slurries, if notalready provided as part of the specifications of the product when soldmay easily be determined by conventional methods.

The number of measurements taken using the method of the presentinvention during a single CMP polishing procedure is not limited.However, a number of between 3 and 15 is preferred and between 5 and 10is more preferred. If the number is too large, the time period formeasurement between changes becomes too short and since force and COFmeasurements tend to show a short period of adjustment of a second orless, it is desirable to have a long enough test period to yieldreliable data. A time period that is too long is wasteful in that theadvantage of the present invention is to allow multiple measurements ofthe same system under the same conditions except for pressure andrelative velocity and a long period means fewer runs. The length of theperiod for each measurement may be the same or may vary, but equalperiods of measurement for each set of process conditions is preferred.Time periods of between 5 and 70 seconds are preferred and between 10and 40 seconds are more preferred. Measurement of shear and down forcesitself may be done at high frequency for example, cases, above 500 hz.And more preferably 1000 Hz or

Sequences of changes in measurements are not particularly limited.Measurements may proceed by ascending or descending value of eitherrelative velocity or pressure with the other variable maintainedconstant, or they may both be increased or decreased at the same time.One may be increased and the other decreased at the same time or one maybe increased or decreased while the other is kept constant and then theother increased or decreased while the former is kept constant. Thechange may also be entirely random. Specific measurement conditions mayalso be repeated within a single CMP polishing procedure as a way ofverifying whether there is any difference at one point in a CMPpolishing procedure as compared with another point later on.

The minimum difference in pressure conditions between measurements isnot particularly limited but variations of greater than ¼^(th) psi arepreferred. The minimum difference in relative velocity conditionsbetween measurements is not particularly limited but differences greaterthan 0.2 meters per second are preferred.

EXAMPLES

The practice of the present invention is demonstrated without beinglimited by reference to the following practice example:

Example 1

An Araca APD-800 polisher equipped with a single plate shear forcemeasuring device, load sensors beneath the CMP polishing pad module andstepping motors and fixtures for variation of the pressure applied tothe wafer CMP polishing pad contact was used as the polishing tool andit was equipped with a MMC TRD 100 grit diamond conditioner disc used insitu under a conditioning force of 5.8 lb_(f) with 30 RPM rotation and10 per minute sweep frequency. The polishing pad used was a Rohm andHaas IC1000-k-groove pad. The silica based slurry was introduced at aflow rate of 300 cc/minute. The wafer used was a 200 mm blanket copperwafer. The wafer was polished under these conditions for a total of 150seconds during which the pressure on the wafer, the relative velocity ofthe wafer and CMP polishing pad or both were changed as indicated inTable 1 approximately forty seconds after starting and approximatelyevery thirty seconds thereafter. The results of shear force, normalforce and COF are shown in FIG. 1 and the Stribeck Curve is shown inFIG. 3.

Example 2

Except that the sequence of pressure and relative velocity were as shownin Table 1, and a different 200 mm blanket copper wafer used, a CMPpolishing procedure was carried out in the same way as in Example 1. Theresults of shear force, normal force and COF are shown in FIG. 2. TheStribeck Curve is shown in FIG. 4.

TABLE 1 Relative Wafer Pressure Velocity Polishing Carrier Time fromExample # Step (PSI) (m/s) Pad RPM RPM start (sec) 1 1 2.5 1 42 39 0 21.5 1 42 39 37 3 2.0 1 42 39 67 4 2.5 0.6 25 23 97 5 2.5 1 42 39 127 2 11.5 1 42 39 0 2 2.5 1 42 39 35 3 2.0 1 42 39 68 4 2.5 0.6 25 23 97 5 1.51 42 39 127

FIG. 1 is a graph of measurement of the Shear Force, Normal Force andCOF measured during a CMP polishing operation during which pressure andrelative velocity were varied by specific amounts at specific intervals.

FIG. 2 is a graph of measurement of the Shear Force, Normal Force andCOF measured during a CMP polishing operation during which pressure andrelative velocity were varied by specific amounts at specific.

FIG. 3 is the Stribeck Curve for FIG. 1.

FIG. 4 is the Stribeck Curve for FIG. 2.

EFFECTS OF THE INVENTION

As can be observed clearly from the results in FIG. 1 and FIG. 2, clearconsistent values for shear force and normal force can be obtained overapproximately 30 second intervals. Moreover, changes in either pressure,relative velocity or both can be made within one or two seconds, a smallfraction of the total interval in this case, and stable measurementvalues for shear force, normal force and COF require little time toachieve following the aforesaid change in conditions. Between the twoseparate runs, a fairly close correlation between force values wasobtained for the two different but very similar discs run under close toidentical conditions. This suggests that by shortening the interval andrunning the same conditions for CMP polishing with very similar discsextensive information that could be used to generate very complete anddetailed Stribeck curves can be obtained for any system with a minimumof expense, inconvenience or inconsistency. Given that the presentmethod makes it possible to obtain far better data for Stribeck curvesfar more easily, it also makes determination of the lubricationmechanism of CMP polishing systems much easier and more accessible tooperators and researchers.

1. A method of determining the shear force and normal force between aCMP wafer and a CMP polishing pad at multiple applied pressures andrelative velocities of the CMP wafer and the CMP polishing pad whereinthe CMP polishing tool is capable of measuring the said shear force andnormal force simultaneously and continuously by force measurement meansduring CMP polishing and of allowing the alteration during CMP polishingof the pressure applied to the CMP wafer and CMP polishing pad contactsurface, the relative velocity between the CMP wafer and the CMPpolishing pad or both simultaneously in determinable amounts.
 2. Themethod determining the shear force and normal force between a CMP waferand a CMP polishing pad at multiple applied pressures and relativevelocities of the CMP wafer and the CMP polishing pad according to claim1 wherein the shear force and normal force data are used to determinethe coefficient of friction of the surface of the CMP wafer and thesurface of the CMP polishing pad.
 3. The method determining the shearforce and normal force between a CMP wafer and a CMP polishing pad atmultiple applied pressures and relative velocities of the CMP wafer andthe CMP polishing pad according to claim 2 wherein the COF figure for agiven time interval during the CMP polishing process thus obtained isused together with data reflecting the pressure applied to the CMP wafersurface and the CMP polishing pad as well as the relative velocity ofthe CMP wafer surface and CMP polishing pad corresponding to the sameinterval are used to calculate and plot a Sommerfeld number and togetherwith the corresponding COF value a Stribeck Curve for the system createdby said CMP wafer and CMP polishing pad.
 4. The method determining theshear force and normal force between a CMP wafer and a CMP polishing padat multiple applied pressures and relative velocities of the CMP waferand the CMP polishing pad according to claim 1 wherein the CMP polishingtool determines and reports the shear force between the wafer head andthe polishing pad by means of a plate positioned above the wafer headand from which the wafer head and its supporting apparatus hang, or uponwhich they rest, said plate connected to the framework of the CMPpolishing tool by low friction motion means capable of sliding in adirection perpendicular to the line between the center of the polishingpad and the center of the wafer head, and a load cell sensor firmlyfixed to the framework of the CMP polishing tool or other immovablestructure and positioned to contact and determine the force from theleading edge of said plate when the CMP polishing tool is in operationand the wafer head is in contact with the polishing pad, the signalsthus obtained reporting the shear force and additionally in which loadcells are attached to and support the bottom of the module of thepolishing pad of the CMP polishing tool to determine the normal force,and the normal force and shear force thus obtained may be used tocalculate the coefficient of friction between the wafer head and thepolishing pad.
 5. The method of determining the shear force and normalforce between a CMP wafer and a CMP polishing pad at multiple appliedpressures and relative velocities of the CMP wafer and the CMP polishingpad according to claim 4 wherein the pressure and relative velocity maybe varied separately or together for the desired length of time.
 6. Themethod of determining the shear force and normal force between a CMPwafer and a CMP polishing pad at multiple applied pressures and relativevelocities of the CMP wafer and the CMP polishing pad according to claim1 wherein the CMP polishing tool determines two perpendicular forcecomponents of shear force and the resulting shear force by means of twoplates positioned above the wafer head from which the wafer head and itssupporting apparatus hang, or upon which they rest, one plate connectedto the framework of said CMP polishing tool by low friction rails, theother said plate connected to the first plate by low friction railsallowing the other said plate to slide in a direction perpendicular tothe motion of the first said plate, load cells sensor firmly fixed tothe framework of the CMP polishing tool or other immovable structure andpositioned to contact and determine force from the leading edge of saidplate when the CMP polishing tool is in operation and the wafer head isin contact with the polishing pad, the signals of the load cell sensorsthus obtained reporting the components of shear force, and in which loadcell sensors are attached to and support the bottom of the CMP polishingpad module of the CMP polishing tool to determine the normal force, andthe shear force and the normal force thus obtained are delivered to adata processing means to calculate the coefficient of friction.
 7. Themethod of determining the shear force and normal force between a CMPwafer and a CMP polishing pad at multiple applied pressures and relativevelocities of the CMP wafer and the CMP polishing pad according to claim6 wherein the pressure and relative velocity may be varied separately ortogether for at the beginning or end of a fixed time period.
 8. Themethod of determining the shear force and normal force between a CMPwafer and a CMP polishing pad at multiple applied pressures and relativevelocities of the CMP wafer and the CMP polishing pad according to claim1 wherein the said length of the said time period is between 5 secondsand 70 seconds.
 9. The method of determining the shear force and normalforce between a CMP wafer and a CMP polishing pad at multiple appliedpressures and relative velocities of the CMP wafer and the CMP polishingpad according to claim 1 wherein the length of the said time period isbetween 10 and 40 seconds.
 10. The method of determining the shear forceand normal force between a CMP wafer and a CMP polishing pad at multipleapplied pressures and relative velocities of the CMP wafer and the CMPpolishing pad according to claim 1 wherein the said time periods areequal.